getting caught short

I don't know about the rest of you but this is an increasingly frustrating thing for me. I always make sure I've 'been' before a run (1's and 2's) but no matter what, I find I am desperate need of a bathroom after about 5 miles and public facilities are all locked up around here. When I do find somewhere I find I have the runs quite badly (pardon the irony here). I did try and search here but obviously words like runs come up with a lot of results. I do have a shortened intestine and colon due to a motorcycle crash in my younger days but thats never caused me any bother. Did a half at the weekend and thankfully that was ok. Today was a nightmare despite having only a light lunch and waiting 2 hrs before going out.